Group B Streptococci (GBS) are the leading cause of neonatal sepsis and meningitis. Maternal IgG antibodies to the GBS polysaccharide (PS) protect the neonate from invasive GBS disease. Such antibodies are deficient in mothers of infants who develop GBS type III disease. A case control study was designed by NICHD to confirm the amounts of antibody needed for protection. The last annual report described a new method of serotyping GBS and examined isolates from various parts of the U.S. to look at serotype distribution for use in the associated antibody study of GBS carriers versus GBS cases. Statistical analysis of serotyping data as well as the level of antibodies in maternal and cord sera for GBS type Ia are being carried out. Paired maternal and cord sera from different regions of the United States were analyzed for the presence of naturally occurring antibodies against GBS type Ia polysaccharide. The serum samples were taken from non-colonized and colonized women to determine if there is a correlation between carriage and antibody levels for this particular polysaccharide. Measurements of antibody concentrations for GBS type III have proven to be more challenging. GBS type III PS purified by two different procedures as well as GBS type III PS conjugated to a protein carrier, when used in the measurement of antibodies among non immunized adults, have all yielded different antibody estimates. In one GBS purification method, GBS culture supernatant is used as the starting material to purify GBS type III PS, while another uses the bacterial pellet and alkali treatment to remove the group antigen followed by reacetylation. We have prepared GBS III PS from concentrated culture supernatants with essentially no group antigen contamination (as indicated by NMR) without harsh treatment. Earlier work in our laboratory has shown that conjugation of the GBS III PS to albumin or biotin changes some of the PS epitopes. We are investigating how differences in methods of PS preparation and conjugation relate to the observed differences in antibody estimates. A series of monoclonal antibodies against pneumococcal type 14 and GBS III PS were used to evaluate epitopes present on the two polysaccharides. It is clear that different epitopes on GBS III PS are being exposed with different chemical modifications. Conjugations are being done by different procedures and The aim of this study will be to determine the best antigen suitable for use in measuring antibodies specific to GBS III in an ELISA.